Hey, guys and gals. As have many of you, I've been modifying mufflers for more power, and in three cases, modifying for less noise. I think I've hit on the easiest mod, while still keeping power output high. Many years ago, I gutted a tall spraycan, and built my own add-on can, with fiberglass packing, and a screen-door wire mesh inner pipe. Now-clearly we don't want to do that on our WRr's, but I found that placing curves in the inner wire mesh (IE not a straight tube) massively reduced the bark of that two-stroke. That led to tonight's very quick test. I had 1/4" wire mesh on hand. I cut a length of 4 feet by 4 inches. I then tapered 3 of those feet from 1 inch wide to 4 inches wide. When rolled into a two-inch roll, this gave me a cone-shaped interior. It has a shape similar to looking into the spark arrestor. When placed inside my brand-new and very loud PC4 muffler, so that the cone is widest toward the engine, the nasty sharp-edged bark at WOT is reduced very greatly. There's still a nice low rumble, which I believe means I've still got good flow. (It's raining snow, so I won't be riding for a while yet...) I'll be making a slightly longer version tomorrow, and plan to take picks and a before and after video. I'll use my Radio Shack DB meter, too. I hope that this mod will give me appropriately quiet street operation, and still give me the power boost that I want.
I'm always interested in stuff like this but I think your post needs some pictures or sketches - not easy to picture what you're saying.
+1 on what blue and yellow said..... Not that I don't believe you, but I am skeptical. I would love to see dyno #s for comparison. Seems to me cutting back on flow has to adversely affect performance, but there may be an acceptable trade off. I will watch intently and curiously.....
Well, the results were a roaring, errr-a whispering sucess. With the raw FMF Megabomb feeding into an FMF PC4, I'd have gotten a ticket just idling at the side of the road. With the hardware cloth insert, I could, seriously, accel at a hard rate past a cop without a second glance. It's somewhat louder than stock, but much smoother than my drilled-out stock muffler. The videos linked below were recorded at a set volume level, so each vid could be accurately compared, but it doesn't reflect the extremely loud snap from each exhaust pulse in the raw setup. I revved the raw muffler much less hard than I did the tamed muffler, so keep that in mind when viewing the videos. OF COURSE there will be less power. All mufflers reduce exhaust flow. This mod is about being able to fine-tune the exhaust for road use, while maximizing power. Hopefully I'll be able to post some riding impressions and added-top-end speeds in a month or so. The gaping maw of the stock FMF PC4 muffler: The 1/4" hardware cloth before coiling: An exhaust-pulses' view of the insert: This side view shows how the density of cloth increases from the left/front, to the exit/right: The videos: http://www.youtube.com/watch?v=hkzE2PNC7nU http://www.youtube.com/watch?v=erfIn9MGCbY
Love your ingenuity!! I'm gonna give this a shot on my BigGun and see what I think....Contrary to popular belief I would like my bike to be quieter if the power loss is nominal. Good job! Keep us posted on how the screen holds up....
I have an FMF Titanium4. I took perforated stianless steel , 1/4 " holes , 3/16 " apart and cut a 2" wide strip 20" long and twisted it a full turn. I put this thru the core and put a disc I cut of it over the end under the tip.
I tried this in my Two Bros on my SV650, but couldn't get twists straight enough to get down the muffler! I think this is probably a better option for power, though.
I was also experimenting with the back pressure. Mine has different diameter tips. The biggest tip gives better bottom end , the smaller one gives better top end , but is louder. I found a happy medium like it is now.With the bgger tip. With a second layer on the end with the holes halfway crossed its louder.
Thanks for the pictures! Should work well - all the small wires should help break up and diffuse the initial soundwave thump coming from the cylinder. With a diffusion principle like this you're probably going to loose out on a little hp compared to the very best tuned exhausts on the market (reflective soundwaves can actually help the engine breath if you didn't now it). But if all you wanted to do was to reduce weight while keeping the sound level down (which would be what I'd want as well) it should work well!
wow, with pics, this is such a great post... Im going to do this to make my bike as quiet as possible I have a new found respect for quiet trail riding, I find I enjoy the engine more and the sights and scenes much better when riding with a stock exhaust someboy hacked my original 88 xr6 muffler, the gap or hole is bigger than the pc4 I had even without the spark arrestor, after taking off the pc4 and selling it I installed my oem setup and the difference was amazing...especially accelerating however on decel the damn baffle less oem muffler has this AWFUL metallic sucking sound that is beyond attrocious and I had forgotten about it, so Im looking for a cheap diy solution to fix internally JUST LIKE THIS so thanks so much perfect timing and kudos for your effort, its much appreciated christian ps just saw the vids, IMPRESSIVE, what was mx db´s on the modified pc4? thanks
Well, I couldn't wait, I went for a short ride. I decided that the packing was too quiet, so I clipped off 4" length from the header pipe end, and I took out 6" width from the interior. This makes the idle louder, and low-speed riding isn't whisper-quiet, but still suitable for neighborhood riding. I'm really loving the increased torque just above idle with the megabomb header. Unfortunately, even with the additional removal, top speed stuck at 79 mph in my quick test. At speed, the muffler is much quieter, and very smooth. So even more material could be removed. At this point, I think I'll try using a square piece of hardware cloth, rather than triangular, to give two to three wraps extending the length of the muffler, with an open space inside for uninterrupted flow.
Thanks a lot man!! Please keep up the testing and the improvement! I believe you're very close to find the sweet spot where both the sound and the performance loss is optimal! and when you found it please make a detailed step by step instructions with pictures so that we newbies can implement it too
Thats pretty small gauge wire to be in the direct path of the hot exhaust. I'd bet on an extended highspeed run there will be molten projectiles flying out the pipe.
I also thought about the same thing, but maybe a more heat resistant/strong material might be used to replace the gauge wire? In the end, this is just a trial phase for perfection :) when the desired sound and the power is achieved, the final production with better quality materials can begin! :) Sent from my iPad using Tapatalk HD
What stops the mesh from being blown out of the muffler, the pressure from it being coiled? Im interested in quieting down my new DG muffler.
The temperature in the can will be around 1400 f. Well below the melting point of steel. Loud pipes close trails.
